efficacy
B2Substantiv/US /ˈɛfɪkˌæsiː/ ĔF-ĭk-ăs-ē; UK /ˈɛfɪkˌæsiː/ ĔF-ĭk-ăs-ē/
Power to produce effects; operation or energy of an agent or force; production of the effect intended; as, the efficacy of medicine in counteracting disease; the efficacy of prayer.
